Random access preamble coding for initiation of wireless mobile communications sessions

ABSTRACT

A wireless communications network, including a base station ( 10 ) and wireless units (UE), is disclosed. The wireless units (UE) request a connection with the base station ( 10 ) by the transmission of a preamble within time slots designated by the base station ( 10 ). The disclosed preambles are Walsh Hadamard code symbols, repeated a number of times so as to have the same length as a cell-specific scrambling code. The wireless unit (UE) requesting a connection pseudo-randomly selects a time slot from those available, and one of the Walsh Hadamard code symbols, replicates the code symbol into a spread interleaved bitstream, scrambles this bitstream and transmits it to the base station ( 10 ). Upon receipt, the base station ( 10 ) applies the incoming bitstream to a matched filter ( 98 ) to descramble the signal, following which the symbol is de-interleaved by way of a sequence of delay lines ( 100 ). Despreaders ( 102 ) generate each bit of the symbol from corresponding taps of the delay lines ( 100 ), and the symbol is applied to a correlator ( 104, 126, 136 ) to determine the transmitted preamble.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit, under 35 U.S.C. §119(e)(1),of U.S. Provisional Applications No. 60/138,713 (TI-29324PS), filed Jun.11, 1999, No. 60/139,334 (TI-29324PS1), filed Jun. 15, 1999, and No.60/142,889 (TI-29324PS2), filed Jul. 8, 1999, all incorporated herein bythis reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] This invention is in the field of mobile wireless communications,and is more specifically directed to the initiation of multiple accesscommunications sessions.

[0004] The popularity of mobile wireless communications has increaseddramatically over recent years. It is expected that his technology willbecome even more popular in the foreseeable future, both in modern urbansettings and also in rural or developing regions that are not wellserved by line-based telephone systems. This increasing wireless trafficstrains the available communications bandwidth for a given level ofsystem infrastructure. As a result, there is substantial interest inincreasing bandwidth utilization of wireless communications system tohandle this growth in traffic.

[0005] Modem digital communications technology utilizes multiple-accesstechniques to increase bandwidth utilization, and thus to carry morewireless traffic. Under current approaches, both time division multipleaccess (TDMA) and code division multiple access (CDMA) techniques areused in the art to enable the simultaneous operation of multiplecommunications conversations, or wireless “connections”. For purposes ofthis description, the term “conversations” refers to either voicecommunications, data communications, or any type of digitalcommunications. As evident from the name, TDMA communications areperformed by the assignment of time slots to each of multiplecommunications, with each conversation transmitted alternately overshort time periods. CDMA technology, on the other hand, permits multiplecommunications sessions to be transmitted simultaneously in both timeand frequency, by modulating the signal with a specified code. Onreceipt, application of the code will recover the correspondingconversation, to the exclusion of the other simultaneously receivedconversations.

[0006] As is fundamental in the art, a single base station in a wirelesscommunications network conducts communications sessions with multiplemobile wireless transmissions in an area of coverage, or “cell”. Inaddition, each base station is aware of the remaining bandwidthavailable for new communications sessions that may be initiated relativeto a wireless unit within its cell. In this regard, the base station isaware of the presence of those mobile wireless units that are turned onand within its cell, and also of the identity of those units, regardlessof whether the units are currently connected in a conversation. In thisway, wireless units may be called by another party from anywhere in thetelephone network, and the wireless units themselves may initiate aconnection by placing a call.

[0007] In order for a wireless unit to place a call to a particulartelephone number, it must send a request for a connection to the basestation. An initiation sequence is then carried out, according toconventional systems, in which the channel for the desiredcommunications is assigned by the base station and acknowledged by thewireless unit.

[0008] For example, in a CDMA system, the base station and wireless unitmust “agree” upon a modulation code to be used in the communicationslink between these two stations. In conventional CDMA systems, the codesare not determined a priori, given the transient nature of wirelessunits within a base station coverage area. As such, techniques have beendeveloped by way of which the wireless units and base station maycommunicate prior to the assignment of a modulation code. According to awidely used technique for this initialization, the base stationperiodically broadcasts signals that indicate the number and position ofreserved time slots within a communications frame for initialization, toeach of the wireless units in its area that are not currently connected.These broadcast signals are received by each wireless unit, so that, inone of these time slots, the unit may send a signal to the base stationto request a connection. This request signal is commonly referred to asa “preamble,” following which the message part of the transmission iscommunicated.

[0009] It is quite likely, however, that multiple wireless units may tryto establish communications at the same time, and may therefore besimultaneously sending preambles within the same time slot. As such,conventional CDMA wireless communications systems specify a set ofmodulation codes from which the wireless unit selects a code to requesta connection. The codes in the set are orthogonal relative to oneanother, in the sense that the base station can resolve the sources ofsimultaneously received messages encoded by different ones of the set ofmodulation codes. Because the requesting wireless unit typically selectsa modulation code in a pseudo-random manner, these channel selectioncodes are typically referred to as “random access” codes. These randomaccess codes greatly reduce the probability of a collision between two(or more) wireless units in a coverage area requesting a connection atthe same time slot. For example, if eight time slots are available forrequesting a connection, using one of sixteen available random accesscodes, the likelihood of a collision between two wireless units thatrequest a connection is reduced from one in eight to one in 128.

[0010] An example of this random access approach uses a 256-chipspreading code in the generation of the preamble part of thetransmission. This conventional approach is described in TechnicalSpecification TS 25.213 V2.1.0: Spreading and Modulation (3rd GenerationPartnership Project, 1999). To request a communications sessionaccording to this approach, a wireless unit randomly selects one ofsixteen signature symbols for its preamble. The signature consists of asixteen-symbol sequence of plus or minus the complex value A=1+j. Oneexample of a sixteen symbol signature is [A, A, A, −A, −A, −A, A, −A,−A, A, A, −A, A, −A A A]. Each symbol in this preamble is then spreadinto 256 consecutive chips, following which the spread preamble ismodulated and transmitted to the base station by the requesting wirelessunit

[0011] The mobile nature of the wireless units presents certaindifficulties to the resolution of simultaneous encoded request signals,however. Although random access codes, such as the 256-chip spread codedrandom access preamble noted above, provide signatures that aretheoretically orthogonal, this orthogonality presumes simultaneousreceipt at the base station. As noted above, preambles aresimultaneously transmitted by mobile units in the time slots specifiedby the base station. However, simultaneously transmitted preambles fromwidely differing distances in the cell will not simultaneously arrive atthe base station. According to the conventional 256-chip spread codedapproach, coded signatures are not necessarily orthogonal when onepreamble is significantly time-shifted relative to another. In otherwords, time-shifted preambles coded according to this conventionalapproach will cross-correlate with one another. As such, in somecircumstances, conventional CDMA base stations may not always be able toresolve different random access codes from multiple wireless units.

[0012] This cross-correlation of random access codes received fromvarying transmission distances has been addressed by prior techniques.For example, a so-called “long” code has been developed which uses areal-valued version of the uplink spreading code to spread the wirelessunit signature over a much longer preamble. The length of the preambleis, in this approach, selected to be significantly longer than thegreatest time delay expected within a given cell. This long code isderived simply by spreading each bit of a sixteen-bit Gold codesignature symbol A over a number of chips, for example 256 chips; inthis case, the sixteen-bit symbol becomes sixteen sequences of 256-chipvalues, for a total length of 4096 chips. This longer preamble greatlyreduces the cross-correlation between orthogonal signatures that arereceived at the maximum delay (and thus the maximum differentialdistance) relative to one another.

[0013] However, it has been observed that this long code approachremains vulnerable to velocity variations between requesting mobilewireless units. The well-known Doppler effect refers to the shift infrequency that results for a moving source of periodic signals. For thecase of mobile wireless units in a moving automobile, train, orespecially an airplane, the Doppler shift causes a phase shift thataccumulates over the transmission length of the request. As noted above,the conventional “long” random access code has a length of 4096 chips(i.e., sixteen symbols of 256 chips each), over which the orthogonalsignatures are analyzed to resolve different wireless units. Because ofthis code length, the accumulated Doppler phase shift can causecross-correlation among codes, so that the base station may not be ableto resolve simultaneous transmission requests.

[0014] Other approaches for encoding random access channel preambleshave been derived to address the problem of Doppler shifts on thetransmitted signals. One approach utilizes a differential encodingtechnique, in which the signature is determined by the differencesbetween adjacent symbols in the preamble. Some level ofcross-correlation for time-delayed signals has been observed for thisdifferential approach, rendering it somewhat vulnerable to differencesin distance between simultaneously-transmitting mobile wireless units.Because of this vulnerability, coherent encoding over a long (e.g., 4096chip) preamble has been used for slowly moving or stationarytransmitters to provide adequate orthogonality for variations intransmission distance, while rapidly moving mobile units utilize thedifferential coding. Of course, the implementation of different randomaccess channel encoding for mobile units of different velocitiessignificantly increases the complexity of transmitters and basestations.

[0015] Another approach uses segmented non-coherent decoding forfast-moving transmitters, in which the receiver decodes the preamble inshorter segments of symbols, for example four segments of four symbolseach. According to this technique, however, the segments are notorthogonal relative to one another.

BRIEF SUMMARY OF THE INVENTION

[0016] It is therefore an object of the present invention to provide arandom access channel resolution method that is robust for mobilewireless transmissions from varying distances within a cell and also fortransmissions from units that are widely varying in velocity.

[0017] It is a further object of the present invention to provide such amethod in which the preamble encoding and decoding can be implemented ina computationally efficient manner.

[0018] It is a further object of the present invention to provide such amethod in which quite large frequency offsets due to moving transmittersmay be tolerated in the establishment of a wireless communicationssession.

[0019] Other objects and advantages of the present invention will beapparent to those of ordinary skill in the art having reference to thefollowing specification together with its drawings.

[0020] The present invention may be implemented into a wirelesscommunications system in which the transmission preamble is based upon aWalsh Hadamard code. Spreading is accomplished by repeating the codesymbol a plurality of times to create a preamble of a lengthcorresponding to that of a long code, creating a preamble of orthogonalsymbols that are repeated in a spread fashion. The preamble ismultiplied by a cell-specific long code, and the process is reversedupon receipt at the base station to recover the preamble.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0021]FIG. 1 is an electrical diagram, in block form, of a cell of awireless communications system, according to the preferred embodiment ofthe invention.

[0022]FIG. 2 is an electrical diagram, in block form, of a mobilewireless telephone in the wireless communications system of FIG. 1,according to the preferred embodiment of the invention.

[0023]FIG. 3 is an electrical diagram, in block form, of a base stationin the wireless communications system of FIG. 1, according to thepreferred embodiment of the invention.

[0024]FIG. 4 is a functional diagram, in schematic form, illustratingdata flow in the encoding of wireless communications.

[0025]FIG. 5 is an illustration of the arrangement of code symbols forgenerating a preamble, according to the preferred embodiment of theinvention.

[0026]FIG. 6 is a flow diagram illustrating the operation of a wirelessunit and a base station, according to the preferred embodiment of theinvention.

[0027]FIG. 7 is an electrical diagram, in block form, of chip-ratedemodulation and despreading circuitry in a base station, according to afirst preferred embodiment of the invention.

[0028]FIG. 8 is an electrical diagram, in block form, of chip-ratedemodulation and despreading circuitry in a base station, according to asecond preferred embodiment of the invention.

[0029]FIG. 9 is an electrical diagram, in block form, of chip-ratedemodulation and despreading circuitry in a base station, according to athird preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described in connection with awireless voice and data communications system, particularly in the casewhere the wireless units are mobile within an area of coverage, or“cell”. Further, the particular preferred embodiment of the inventionwill be described relative to such a system in which multiplecommunications of the Code Division Multiple Access (CDMA) type arehandled by a base station in the cell. It is contemplated, however, thatthe present invention may also be used with other communicationssystems, for example mobile wireless communications using Time DivisionMultiple Access (TDMA) or other spread spectrum or broadbandtechnologies, as well as other applications. It is to be understood,therefore, that the following description is presented by way of exampleonly, and is not intended to limit the scope of the present invention asclaimed.

[0031] An example of a deployment of a wireless communications system,according to the preferred embodiment of the invention, is illustratedin FIG. 1. As shown in FIG. 1, base station 10 is located somewhatcentrally within an area of coverage, or cell, 14. Base station 10, asis conventional in the art, is a fixed facility which transmits andreceives broadband, or spread spectrum, wireless communications to andfrom wireless units UE that are physically located within cell 14. Asshown in FIG. 1, and is typical in the art, wireless units UE are mobilewireless units, such as digital cellular telephones. The number ofwireless units UE within cell 14 may vary widely, depending upon thetime of day, day of the week, and other events that can affect wirelesstelephone density within cell 14.

[0032] Typically, a large fraction of the wireless units UE within cell14 are mobile units, and as such may be anywhere within the transmissionarea of cell 14 at any given point in time. For example, wireless unitUE₂ is quite close to base station 10, while wireless unit UE_(n) isrelatively distant from base station 10, near the edge of cell 14.Furthermore, wireless units UE may be moving within cell 14. Forexample, wireless unit UE₁ is moving away from base station 10 atvelocity v. These variations in distance among wireless units UE, andtheir velocities of travel, present difficulties in the resolving ofpreamble codes for connection requests, according to conventionaltechniques. As will be described below, the preamble coding according tothe preferred embodiment of the invention efficiently provides goodresolution of coded preambles transmitted from different distances andat significant velocities.

[0033] The communications carried out between base station 10 andwireless units UE are, in this example, telephonic conversations betweenone of wireless units UE and another telephone set elsewhere in thetelephone network. Base station 10 therefore includes the appropriatecircuitry for effecting broadband communications with wireless units UE,as will be described in further detail below; additionally, base station10 includes switching system 12 that carries out some level of switchingof the communications links between individual wireless units UE and thepublic switched telephone network (PSTN).

[0034] Wireless units UE, as noted above, correspond to mobile wirelesstelephone sets. FIG. 2 is an electrical diagram, in block form, of theelectronic architecture of a typical mobile wireless unit UE_(j) (theindex j referring generically to one of the wireless units UE shown inFIG. 1). It is contemplated, of course, that different ones of thewireless units UE in the overall system, such as shown in FIG. 1, may beconstructed according to different architectures. As such, thearchitecture of the construction of wireless unit UE_(j) shown in FIG. 2is provided by way of example only, it being understood that such otheralternative architectures may also be used in connection with thepresent invention.

[0035] The exemplary architecture illustrated in FIG. 2 corresponds to aso-called “second generation”, or “2G” baseband architecture, such as istypically used to carry out TDMA and CDMA broadband communications.Radio subsystem 22 of wireless unit UE_(j) is directly connected toantenna A, and handles the power amplification and analog processing ofsignals transmitted and received over antenna A. On the transmit side,modulator 27 in radio subsystem 22 receives the signals to betransmitted from RF (radio frequency) interface circuitry 30, andgenerates a broadband modulated analog signal, under the control ofsynthesizer 25. Power amplifier 21 amplifies the output of modulator 27for transmission via antenna A. On the receive side, incoming signalsfrom antenna A are received by receiver 23, filtered and processed underthe control of synthesizer 25, and forwarded to RF interface circuitry30.

[0036] RF interface circuitry 30 processes both incoming and outgoingsignals within the analog baseband of wireless unit UE_(j). On thetransmit side, RF interface circuitry 30 receives digital signals fromdigital signal processor (DSP) 32, and performs the appropriatefiltering and phase modulation appropriate for the particulartransmission protocol. For example, multiple channels of encoded digitalbitstreams may be forwarded to RF interface circuitry 30 by DSP 32. RFinterface circuitry 30 converts these digital data into analog signals,phase-shifting selected converted bitstreams to provide both in-phase(I) and quadrature (Q) analog signal components, and applies analogfiltering as appropriate to the signals as handed off to modulator 27 inradio subsystem 22 described above.

[0037] On the receive side, RF interface circuitry 30 converts theanalog signal received by receiver 23 of radio subsystem 22 into theappropriate digital format for processing by DSP 32. For example, thein-phase (I) and quadrature (Q) components of the received signal areseparated and filtered. Analog to digital conversion is then carried outby RF interface circuitry 30, so that digital bitstreams correspondingto the separated and filtered components of the received signal may bereceived by DSP 32.

[0038] DSP 32 executes the appropriate digital signal processing uponboth the signals to be transmitted and those received. In this regard,DSP 32 is connected to audio interface 34, which in turn is coupled tomicrophone M and speaker S for input and output, respectively. Audiointerface 34 includes the necessary analog-to-digital conversioncircuitry and filtering for generating a sampled bitstream digitalsignal based upon the sound received by microphone M, and converselyincludes digital-to-analog conversion circuitry, filtering, andamplification for driving speaker S with an analog signal correspondingto the received and processed communications.

[0039] The digital functions performed by DSP 32 will depend, of course,upon the communications protocol used by wireless unit UE_(j). On thereceive side, DSP 32 will perform such functions as channel decoding ofthe data from RF interface circuitry 30 to retrieve a data signal fromthe digitally spread signal received, followed by the decoding of thespeech symbols from the channel decoded data using techniques such asinverse discrete Fourier transforms (IDFT) and the like. Equalization,error correction, and decryption processes are also performed upon thereceived signal as appropriate. The resulting signal processed by DSP 32on the receive side is then forwarded to audio interface 34, foramplification and output over speaker S.

[0040] On the transmit side, substantially the converse operations areapplied. The incoming digitally sampled voice input from microphone Mvia audio interface 34 is encoded into symbols, for example by way of aDFT operation, and the symbols are then encoded into a digital spreadspectrum signal by the application of channel codes. Scrambling or otherencryption processing is then performed, along with the necessarypre-equalization and other filtering. The resulting digital signal isthen forwarded to RF interface circuitry 30, as noted above.

[0041] According to the preferred embodiment of the present invention,DSP 32 is operable to generate preamble codes to be transmitted bywireless unit UE_(j). These preamble codes are transmitted over antennaA to request the initiation of a communications session, such as awireless telephone conversation. These orthogonal preamble codes areselected, according to this preferred embodiment of the invention, to beresolvable over a wide range of distances of wireless unit UE_(j) frombase station 10 (FIG. 1), and in the event that wireless unit UE_(j) isbeing used in a rapidly traveling conveyance such as an automobile,train, or airplane. The generation of these preambles will be describedin further detail below.

[0042] In this regard, DSP 32 preferably has a significant amount ofprocessing capacity to handle the digital processing necessary for boththe transmit and receive operations. An example of a suitable digitalsignal processor for use as DSP 32 is the TMS320c5x family of digitalsignal processors available from Texas Instruments Incorporated.

[0043] Other support circuitry is also provided within wireless unitUE_(j) as shown in FIG. 2. In this example, microcontroller 36 handlesthe control of wireless unit UE_(j) other than the data path. Suchcontrol functions include resource management, operating system control,and control of the human interface; in this regard, microcontroller 36operates with such functions as flash memory 33 (for storage of theoperating system and user preferences), SIM card 35 (for add-onfunctionality), keypad 37, and user display 38. In addition, wirelessunit UE_(j) also includes battery interface and power control subsystem31, as shown in FIG. 1, for monitoring the status of the battery forwireless unit UE_(j), and implementing power saving functions such assleep modes, and the like.

[0044] Referring now to FIG. 3, the construction of an example of basestation 10 according to a preferred embodiment of the invention will nowbe described, for the case of a second/third generation base transceiverstation. It will be appreciated by those skilled in the art that thisparticular architecture is provided by way of example only, and thatother base station architectures may be used according to the presentinvention.

[0045] As shown in FIG. 3, base station 10 includes amplifiers 42 fordriving amplified transmission signals over one or more base stationantennae BSA, and for amplifying signals received from those antennaeBSA. RF interface function 44 includes the appropriate transmit andreceive formatting and filtering circuitry. Additionally, RF interfacefunction 44 includes analog-to-digital converters for digitizing theamplified receive signals, and digital-to-analog converters for placingthe transmitted signals into the analog domain. As such, RF interfacefunction 44 communicates digitally with baseband interface 45, whichprovides the appropriate signal formatting between RF interface function44 and baseband device 40.

[0046] Baseband device 40 communicates with the ultimate network, whichmay be of the E1 or T1 class, or a packet network as shown in FIG. 3, byway of physical layer interface 55 and network interface adapter 56.Physical layer interface 55 and network interface adapter 56 areconventional subsystems, selected according to the type of network andcorresponding interface desired for base station 10. In theimplementation of FIG. 1, network interface adapter 56 interfaces withswitching system 12.

[0047] Baseband device 40 performs the digital signal processingfunctions in handling the wireless communications at base station 10. Toperform this function, it is contemplated that baseband device 40 willbe a subsystem including one or more high-performance digital signalprocessor (DSP) devices, such as those of the TMS320c5x and TMS320c6xclass of DSPs available from Texas Instruments Incorporated, along withthe appropriate memory and external functions suitable for handling thedigital processing requirements of base station 10. In FIG. 3, theimplementation of baseband device 40 will be described according to itsvarious functions, rather than by way of its construction, it beingcontemplated that those skilled in the art will be readily able torealize baseband device 40 using such conventional integrated circuitsfrom this functional description, and according to the capacity desiredfor base station 10.

[0048] On the transmit side, baseband device 40 includes encode andmodulate function 54, which is coupled between physical layer interface55 and baseband interface 45, as shown in FIG. 3. Encode and modulatefunction 54 receives digital data from physical layer interface 55, andperforms the appropriate digital processing functions for the particularprotocol. For example, encode and modulate function 54 may first encodethe received digital data into symbols. These symbols are then spread,by way of a spreading code, into a sequence of chips, according to aselected chip rate; the spreading may also include the spreading of thesymbols into multiple subchannels. Typically, a cell-specific scramblingcode is then applied to the spread symbols, so that the receivingwireless unit UE can distinguish transmissions generated by this basestation 10, from those of neighboring cells. Modulation of the spreadsymbols is then performed; commonly, the multiple subchannels are splitinto in-phase (I) and quadrature (Q) groups, so that the eventualmodulated signal includes both components. The spread spectrum signal isthen applied to baseband interface 45, after the appropriate filteringand pre-equalization for channel distortion, for transmission overantennae BSA via RF interface function 44 and amplifiers 42.

[0049] On the receive side, baseband device 40 receives incoming digitalsignals from baseband interface 45, after digitization of the receivedsignals within RF interface function 44. These signals are applied tochip-rate demodulation and despreading function 48, the construction ofwhich will be described in further detail below, and which derives thetransmitted symbols from the digitized received data. Considering thatbase station 10 receives signals over multiple channels, from multiplewireless units UE in its cell 14, channel estimation function 46estimates the random channel variation. Channel estimation function 46and chip-rate demodulation and despreading function 48 each provideoutput to symbol user detection and combining function, in which thedemodulated data are associated with their respective channels,following which symbol decode function 52 decodes the received symbols,for each channel and thus each conversation, into a bit stream suitablefor communication to the network via physical layer interface 55 andnetwork interface function 56.

[0050] As discussed above, the present invention is directed to thegeneration of connection requests by mobile units, such as wirelesstelephone units UE in the example of FIG. 1, and to the receipt anddecoding of such requests by the corresponding base station 10.Referring now to FIGS. 4 and 5, the principle of operation in thegeneration of preambles for requesting connection, according to thepreferred embodiment of the invention, will now be described.

[0051]FIG. 4 illustrates the data flow for a transmitting element, suchas mobile user equipment UE in the system of FIG. 1, for exampleconfigured as shown in FIG. 2. In this example, a data bitstream x(k)corresponds to the symbol stream that is to be transmitted, for exampleas part of the eventual data message. This bitstream x(k) is multiplied,in operation 58, by spreading code h(k). Spreading operation 58 spreadseach bit of bitstream x(k) into multiple “chips”, as known in the art.In effect, spreading operation 58 converts each bit of bitstream x(k)into a series of samples, or chips, modulated by the particular codeh(k), with the chip rate out of operation 58 thus being a multiple ofthe data rate of bitstream x(k). A gain factor β is then applied to thespread output of operation 58 in gain stage 60, to adjust the power ofthe particular channel.

[0052] The channel corresponding to bitstream x(k) is an in-phasecomponent (I) that is then combined, at adder 62, with a quadraturecomponent (Q). As known in the art, the transmission may consist of asingle data channel as shown in FIG. 4, combined by adder 62 with acontrol channel that is at 90° phase relative to the data channel; thisquadrature arrangement permits separation of the data and controlinformation upon receipt. As known in the art, the transmission may alsobe carried out over multiple data channels, each channel receiving adifferent one of a set of orthogonal spreading codes h(k) to permitseparation. The multiple data channels may be grouped into in-phase andquadrature groups, with the groups combined prior to adder 62, as knownin the art. Only a single data channel for bitstream x(k) is shown inFIG. 4, for clarity in this description, it being understood that thoseskilled in the art will be readily able to incorporate the presentinvention into a multiple channel transmission.

[0053] The combined I and Q components from adder 62 are then scrambledby a scrambling code c(k) in operation 64. Scrambling code c(k) iscell-specific, in that all transmissions taking place in the same cell(e.g., cell 14 of FIG. 1) use the same scrambling code. Scrambling codec(k) thus allows each system element to resolve incoming communicationsfor its cell from those that may be received from other cells.Typically, scrambling code c(k) is a “long” code, for example 4096 chipsin length.

[0054] Following scrambling operation 64, the scrambled spread signal isthen modulated for transmission by operations 66, 68 into in-phase andquadrature components, respectively. Given that scrambling code c(k)will generally have complex coefficients, the in-phase and quadratureoutput components from operations 66, 68 will generally not correspondto the in-phase and quadrature input components to adder 62.

[0055] The coding of FIG. 4 applied to transmission is, of course, fullyreversible upon receipt.

[0056] In addition to the voice or data communication payloads,preambles are generated according to the scheme of FIG. 4 by wirelessunits UE to request a connection with base station 10. According to thepresent invention, the particular spreading codes h(k) are selected toprovide orthogonality even in situations where simultaneously requestingwireless units UE are at widely differing distances from base station10, and moving at significant velocities, such as suggested by FIG. 1.

[0057] According to the preferred embodiment of the invention, thespreading codes h(k) applied in operation 58 correspond to repetitionsof a selected one of a set of orthogonal Walsh Hadamard codes. Ineffect, the input bitstream x(k) is assumed to be “1”, so that theoutput of operation 58 is a Walsh Hadamard code symbol itself. Thisspreading code output is then multiplied, in operation 64, by thecell-specific scrambling code. As will become apparent below, theselection of Walsh Hadamard codes is particularly beneficial infacilitating transform operations upon receipt.

[0058] According to an exemplary implementation of the preferredembodiment of the invention, scrambling code c(k) is a 4096 chip segmentof a 2²⁵-1 length, real-valued, Gold code. Preferably, cell-specificscrambling code c(k) is formed in the same manner as the in-phasededicated channel uplink scrambling code, and as such is selected as oneof 256 orthogonal 4096-chip segments of the orthogonal Gold code, withthe 256 codes determined from different initial shift register contentsin such code generation. The resulting scrambling code c(k) is thenassociated with sixteen possible preamble codes h(k), each correspondingto a different Walsh Hadamard code.

[0059] As is well known, length 16 Walsh Hadamard codes h_(m)(k), form=0, 1, . . . 15 are specified as: h₀ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 h₁1 −1 1 −1 1 −1 1 −1 1 −1 1 −1 1 −1 1 −1 h₂ 1 1 −1 −1 1 1 −1 −1 1 1 −1 −11 1 −1 −1 h₃ 1 −1 −1 1 1 −1 −1 1 1 −1 −1 1 1 −1 −1 1 h₄ 1 1 1 1 −1 −1 −1−1 1 1 1 1 −1 −1 −1 −1 h₅ 1 −1 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −1 1 h₆ 1 1−1 −1 −1 −1 1 1 1 1 −1 −1 −1 −1 1 1 h₇ 1 −1 −1 1 −1 1 1 −1 1 −1 −1 1 −11 1 −1 h₈ 1 1 1 1 1 1 1 1 −1 −1 −1 −1 −1 −1 −1 −1 h₉ 1 −1 1 −1 1 −1 1 −1−1 1 −1 1 −1 1 −1 1 h₁₀ 1 1 −1 −1 1 1 −1 −1 −1 −1 1 1 −1 −1 1 1 h₁₁ 1 −1−1 1 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 h₁₂ 1 1 1 1 −1 −1 −1 −1 −1 −1 −1 −1 11 1 1 h₁₃ 1 −1 1 −1 −1 1 −1 1 −1 1 −1 1 1 −1 1 −1 h₁₄ 1 1 −1 −1 −1 −1 11 −1 −1 1 1 1 1 −1 −1 h₁₅ 1 −1 −1 1 −1 1 1 −1 −1 1 1 −1 1 −1 −1 1

[0060] According to this exemplary implementation, the selected preamblecode h(k) is repeated 256 times, in an interleaved fashion as will nowbe described.

[0061] Of course, alternative combinations of preamble code length andnumber of repetitions may equivalently be used. For example, a Hadamardcode of length 32 could be repeated 128 times, to still correspond tothe 4096-chip scrambling code. Scrambling codes of different length mayalso be used, depending upon the application, providing still morecombinations of code length and number of repetitions.

[0062] Consider the set of sixteen Walsh Hadamard codes h_(m)(k), m=0,1, . . . , 15, and the set of 256 scrambling codes c_(n)(k) n=0, 1, . .. , 255, where each code h_(m) is sixteen chips long, and each codec_(n) is 4096 chips long. The m^(th) preamble s_(mn) output by operation64 of FIG. 4, corresponding to the nth scrambling code, may beexpressed:${s_{mn}(k)} = {{c_{n}(k)}{\sum\limits_{i = 0}^{255}{h_{m}\left( {k - {16i}} \right)}}}$

[0063] The summation term:$\sum\limits_{i = 0}^{255}{h_{m}\left( {k - {16i}} \right)}$

[0064] corresponds to 256 repetitions of the length sixteen WalshHadamard code. As shown in FIG. 5, the arrangement of preamble symbol 70according to the preferred embodiment of the invention consists of oneof the sixteen possible Walsh Hadamard code symbols h_(m), repeated 256times to create a 4096-chip preamble. In other words, the first bit isthe same in each of the 256 code symbols h_(m), the second bit is thesame in each of the 256 code symbols h_(m) and so on. This arrangementof preamble symbol 70 is thus in stark contrast to conventional Goldcoded preambles, in which each bit of the Gold code symbol is repeatedover a number of chips, followed by the next bit repeated for thosechips, and so on. Also as shown in FIG. 5 and as noted above, preamblesymbol 70 is then multiplied by the particular cell-specific scramblingcode c_(n), prior to transmission.

[0065] Of course, the number of repetitions of the Walsh Hadamard codesymbol will vary with the length of the “long” code that is to beapplied, and as such the implementation described above and illustratedin FIG. 5 is by way of example only. Another example, corresponding tocurrent standards, utilizes a 3840-chip long code. In this case, thelength sixteen Walsh Hadamard code is repeated 240 times.

[0066] Referring now to FIG. 6, the overall operation of wireless unitUE in combination with base station 10, in requesting a connectionaccording to the preferred embodiment of the invention, will now bedescribed. As will be apparent from the following description, theoperations illustrated in FIG. 6 are primarily performed by DSP 32 inthe architecture of wireless unit UE shown in FIG. 2, according to thispreferred embodiment of the invention; of course, the particular circuitexecuting the operations of FIG. 6 will depend upon the specificarchitecture used to realize wireless unit UE. As shown in FIG. 6, thisoperation begins, in process 72, with wireless unit UE receivingcell-specific scrambling code c_(n) from base station 10, for exampleupon entry of wireless unit UE into cell 14 serviced by base station 10.This cell-specific scrambling code c_(n) is used by wireless unit UE forits transmissions, both the preamble for requesting a connection andalso the eventual payload.

[0067] In process 74, wireless unit UE receives a broadcast message frombase station 10 that indicates the particular periodic time slots withinwhich any wireless unit UE may transmit a preamble in order to request aconnection. As known in the art, this broadcast by base station 10 isperiodic, so that the wireless units UE may receive updates of the timeslots currently available for these requests; of course, depending uponthe instantaneous call traffic within the cell, the number of availabletime slots will vary over tine. In decision 76, wireless unit UE decideswhether its user wishes to place a call; if not (decision 76 is NO),wireless unit UE returns to process 74 to again receive the nextbroadcast of the available time slots for requesting connections, andrepeats decision 76 accordingly.

[0068] Upon the user wishing to place a call (decision 76 is YES),wireless unit UE selects one of the available time slots for issuing therequest, and selects one of the Walsh Hadamard codes h_(m) forconstructing the preamble, both in process 78. According to thepreferred embodiment of the invention, the selection of process 78 isperformed by way of a pseudo-random selection algorithm, in order tominimize the likelihood that another wireless unit UE in the same cell14 will select the same time slot and same Walsh Hadamard code for itsown request. According to the preferred embodiment of the invention asdescribed above, in which sixteen Walsh Hadamard codes h_(m) of lengthsixteen are available, selection process 78 will thus randomly selectone of the sixteen codes h_(m) listed above.

[0069] In process 80, DSP 32 in wireless unit UE spreads the selectedWalsh Hadamard code h_(m) in an interleaved fashion, by repeating thecode symbol a number of times sufficient to match the length of theeventual sampling code. For the present example, in which a 4096-chipscrambling code c_(n) is used, the length sixteen Walsh Hadamard codeh_(m) is repeated 256 times (16 times 256 being 4096), effectivelyspreading the code symbol in an interleaved fashion as described aboverelative to FIG. 5. Process 82 is then performed by wireless unit UE tomultiply the spread code symbol according to the cell-specificscrambling code c_(n) received from base station 10. Furtheroversampling of the scrambled signal may also be applied, as desired.The resulting preamble is then modulated and transmitted by wirelessunit UE to base station 10 during the available time slot that wasselected in process 78.

[0070] Base station 10 receives the transmitted preamble in process 86.The received signal corresponding to this preamble is amplified,converted from analog to digital, filtered, and the like, by circuitrysuch as amplifiers 42, RF interface 44, and baseband interface 46 ofbase station 10 for the exemplary architecture of FIG. 2. The resultingdigital signal is then descrambled, demodulated, and de-spread bychip-rate demodulate and despread function 48 of base station 10, torecover the particular Walsh Hadamard code symbol h_(m) that wasselected and transmitted by wireless unit UE.

[0071]FIG. 7 illustrates an exemplary construction of chip-ratedemodulate and despread function 48 according to the preferredembodiment of the invention, which operates according to the methodillustrated in FIG. 6.

[0072] According to this implementation, the incoming digitized signalis first applied to a series of tapped delay lines 100, forde-interleaving the various interleaved spread. code symbols in process88 according to the preferred embodiment of the invention, as will nowbe described in detail. As shown in FIG. 7 for the example of delay line100 ₀, each of delay lines 100 include a series of delay stages D. Thelength of each delay line 100 is 16 n, where n is the oversamplingfactor. Taps are located prior to the first delay stage D, and prior toevery n delay stages thereafter. The example of delay line 100 ₀ in FIG.7 illustrates an oversampling factor n=2, such that there are two delaystages D between taps. The output of delay line 100 ₀ is applied to theinput of delay line 100 ₁, which is next in sequence, and so on. For thepresent example, in which a length sixteen Walsh Hadamard code is spread256 times, the number of delay lines 100 in chip-rate demodulate anddespread function 48 is 256, as evident by final delay line 100 ₂₅₅ inthe sequence shown.

[0073] The taps from delay lines 100 are routed to appropriate ones ofdespreaders 102. Despreaders 102 constitute circuitry or functionalityfor combining corresponding bits of the incoming bitstream back into thebit values for a code symbol, and in this manner “despread” the numberof chips for each bit back into a single bit value. Additionally,despreaders 102 apply the appropriate coefficients of the cell-specificscrambling code to the incoming bits, to reverse the multiplication ofthe spread code by scrambling code c_(n) that was performed intransmission. In this example of length sixteen Walsh Hadamard codes,sixteen instances of despreaders 102 (i.e., despreaders 102 ₀ through102 ₁₅) are provided, each despreader 102 having a length of 256 asindicated in FIG. 7. According to this preferred embodiment of theinvention, in which the symbol is repeated, the bits within the symbolare interleaved among the repetitions, as described above.De-interleaving process 90 in the flow of FIG. 6 is thus performed byeach despreader 102 receiving one tap from each of the 256 delay lines100, from a tap position corresponding to the position of despreader 102among the series of despreaders 102 ₀ through 102 ₁₅. For example, firstdespreader 102 ₀ receives the first tap from delay line 100 ₀ as shown,and the first tap from each of the 255 other delay lines 100 ₁ through100 ₂₅₅. Second despreader 102 ₁ receives the next tap from delay line100 ₀, after n delay stages D as shown, as well as the second tap fromeach of the 255 other delay lines 100 ₁ through 100 ₂₅₅ as shown. Thisarrangement continues for all of the remaining despreaders 102 ₂ through102 ₁₅ in this example. The combination of the input taps to eachdespreader 102 is thus analyzed to generate an output bit, with thecombination of the outputs of despreaders 102 constituting a sixteen-bitsymbol in this embodiment of the invention.

[0074] The outputs of sixteen despreaders 102 ₀ through 102 ₁₅ areapplied as a sixteen-bit symbol to transform and code correlationfunction 104, which compares this symbol, for example by way ofcorrelation, to each of the possible Walsh Hadamard codes h_(m) in theset, in process 94. In this example, transform and code correlationfunction 104 performs a Walsh Hadamard transform of length 16, andcorrelates this result against the transforms for each of the possiblecodes h_(m). Sixteen outputs are generated, each of which is associatedwith one of the possible codes h_(m), and indicating the extent to whichthe received bitstream correlates with its associated code h_(m). Theseoutputs are then analyzed at base station 10, for example in symbol userdetection and combining function 50 (FIG. 3), to resolve the identity ofthe wireless unit UE that forwarded the request corresponding to thedecoded preamble. Assuming that this decoded preamble is valid, basestation 10 then initiates the requested connection to the requestingwireless unit UE, in process 96, enabling the communication of the voiceor data payload information.

[0075] According to this preferred embodiment of the invention,significant advantages in the resolution of preamble codes are provided.The interleaving of the spread preamble code, illustrated by way ofexample in FIG. 5, provides a short length over which the coded symbolsare coherent, and remain orthogonal. In the above example, each symbolis coherent over sixteen chips (times the applied oversampling factor),repeated 256 times. This short coherency length allows preambles ofrapidly moving mobile units to be reliably resolved, since theaccumulated Doppler phase shift is insignificant over such a short codelength. However, the repetition of the symbols over the long code lengthprovides the ability to resolve preambles transmitted by wireless unitsat widely varying distances within the cell. In the above example, thecode symbol of length sixteen is repeated 256 times, resulting in a4096-chip symbol that can be readily resolved even with significantvariations in receipt delay.

[0076] Additionally, as described above relative to the example of FIG.7, the preamble coding according to the preferred embodiment of theinvention is especially efficient in its decoding. Referring to FIG. 7,each of the despreaders 102 can operate in parallel with one another,such that the entire despreading process 90 (FIG. 6) can be done atonce. It has also been calculated that the expected computationalcomplexity for the preamble coding of the preferred embodiment of theinvention is less than that for conventional Gold coding. As a result,the benefits of the present invention in providing excellent resolutionof preambles over wide distance variations and for rapidly movingtransmitters are obtained at no computational cost, and indeed someimprovement in the computational complexity.

[0077] As noted above, the present invention may be implemented in avariety of architectures and arrangements. In addition, it iscontemplated that the coding and decoding described above may beimplemented in combination with conventional approaches, including theconventional long coherent code, and segmented code, described above. Insuch combinations, it is further contemplated that a base station mayreceive and decode preambles according to the present invention and alsoaccording to these conventional techniques, in which case the basestation may use the approach providing the highest correlation power.

[0078] In this regard, referring now to FIG. 8, the construction ofchip-rate demodulate and despread function 48′ according to a secondpreferred embodiment of the present invention will now be described indetail. This second preferred embodiment of the invention corresponds toa segmented non-coherent decoding of the incoming preamble; in thisparticular example, four segments are each sixty-four symbols long, witheach symbol being a Walsh Hadamard code of length sixteen. Of course,other segment lengths may alternatively be used in combination withdifferent code lengths, as desired. For the example of a 4096 chip longcode and length sixteen Walsh Hadamard codes, alternative segmentlengths and numbers may include eight segments of thirty-two symbolseach, and two segments of 128 symbols each.

[0079] As shown in FIG. 8, the input data stream is again received bydelay lines 100, as in the example of FIG. 7. As before, delay lines 100include 256 delay lines 100 ₀ through 100 ₂₅₅, each having 16 times ndelay stages D therein, where n is the oversampling factor. Delay lines100 are tapped along their length as before, to provide 4096 outputsT(0) through T(4093) in this example. These outputs T are applied in aninterleaved fashion to depsreaders 122 ₀ through 122 ₆₃, each of whichare of length 64 in this embodiment of the invention.

[0080] According to this second preferred embodiment of the invention,the code symbols are considered in segments of sixty-four symbols each,rather than coherently over the entire 4096-chip long code length. Assuch, despreaders 122 receive inputs from only a subset of delay lines100. For example, first despreader 122 ₀ receives the first tap (i.e.,prior to the first delay stage D) from each of the first sixty-fourdelay lines 100 ₀ through 100 ₆₃; according to the nomenclature of FIG.8, these inputs are inputs T(0), T(16), T(32), . . . , up to T(1008).The next despreader 122 ₁ receives the second tap from each of the firstsixty-four delay lines 100 ₀ through 100 ₆₃, namely inputs T(1), T(17),and so on up to T(1009). In this manner, despreaders 122 ₀ through 122₁₅ receive each of the taps from the first sixty-four delay lines 100,namely the first 1024 taps on lines T(0) through T(1023). These firstsixteen despreaders thus despread the interleaved chip samples of thefirst sixty-four repetitions of the length sixteen Walsh Hadamard codesymbol, and thus despread the symbols of the first of four segments,according to this embodiment of the invention.

[0081] The next segment of sixty-four repetitions begins with despreader122 ₁₆, which receives the first taps from each of the next group ofdelay lines 100 (i.e., delay lines 100 ₆₄ through 100 ₁₂₇; these firsttaps are presented on lines T(1024) through T(2032). The remainingdespreaders 122 ₁₆ through 122 ₆₃ are thus arranged in three moresegments, similarly as for the first segment of despreaders 122 ₀through 122 ₁₅, each despreader having a length of sixty-four. To theextent that a segmented cell-specific code was applied in transmission,to segments of sixty-four symbols, the four sets of despreaders 122applied to these symbols divide out the cell-specific code from theirinputs. According to the nomenclature of FIG. 8, the output ofdespreader 122 ₀ is presented on line V(0), the output of despreader 122₁ is presented on line V(1), and so on, with the output of the lastdespreader 122 ₆₃ presented on line V(63).

[0082] According to this example, the sixty-four outputs V(0) throughV(63) from despreaders 122 are then applied, in groups of sixteen torepresent a length sixteen Walsh Hadamard code symbol, to one of fourWalsh Hadamard transform and code correlation functions 124 ₀ through124 ₃. Specifically, first Walsh Hadamard transform and code correlationfunction 124 ₀ receives outputs V(0) through V(15), second WalshHadamard transform and code correlation function 124, receives outputsV(16) through V(31), Walsh Hadamard transform and code correlationfunction 124 ₂ receives outputs V(32) through V(47), and Walsh Hadamardtransform and code correlation function 124 ₃ receives outputs V(48)through V(63). As described above relative to FIG. 7, Walsh Hadamardtransform and code correlation functions 124 transform the incomingsymbol and compare the transformed symbol against the sixteen possiblelength sixteen Walsh Hadamard code values; each function 124 thengenerates sixteen outputs X, each indicative of the degree to which theincoming symbol matches the code value corresponding to the output.

[0083] According to this second preferred embodiment of the invention,outputs X from Walsh Hadamard transform and code correlation functions124 are applied to segmenting logic functions 126 ₀ through 126 ₁₅, todetermine the correspondence to the respective symbol values. Segmentinglogic functions 126 number sixteen in this embodiment, because thenumber of possible Walsh Hadamard code values for a code of sixteenlength is sixteen. In this regard, segmenting logic function 126 ₀corresponds to Walsh Hadamard code value ho indicated above in thetable, and in general segmenting logic function 126 _(m) corresponds toWalsh Hadamard code value h_(m). As shown in FIG. 8, segmenting logicfunction 126 ₀ receives output X(0) from Walsh Hadamard transform andcode correlation function 124 ₀, output X(1) from Walsh Hadamardtransform and code correlation function 124 ₁, output X(2) from WalshHadamard transform and code correlation function 124 ₂, and output X(3)from Walsh Hadamard transform and code correlation function 124 ₃. Eachof these outputs X(0) through X(3) provide an indication of the degreeto which the symbol applied to the corresponding Walsh Hadamardtransform and code correlation function 124 matches Walsh Hadamard codesymbol value h₀. Similarly, the other fifteen segmenting logic functions126 ₁ through 126 ₁₅ receive their corresponding inputs from each of theWalsh Hadamard transform and code correlation functions 124, for theircorresponding symbol.

[0084] According to this second preferred embodiment of the invention,segmenting logic functions 126 each perform a power summation of theamplitude of their input signals. Specifically, for the example ofsegmenting logic function 126 ₀, the power summation corresponds to:

|X(0)|²+|X(16)|²+|X(32)|²+|X(48)|²

[0085] The summation presented by segmenting logic functions 126, foreach of their corresponding Walsh Hadamard code symbols h, provide agood indication of which symbol was transmitted by wireless unit UE asits preamble. The segmented nature of the decoding, according to thisembodiment of the invention, provides additional immunity to Dopplershift effects, as the duration over which coherency is required islimited to sixty-four symbols, while each of the segments contributes tothe code resolution operation.

[0086] Referring now to FIG. 9, the construction of chip-ratedemodulation and despreading function 48″ according to a third preferredembodiment of the invention will now be described. Common elements infunction 48″ as in function 48′ of FIG. 8 are referred to in connectionwith the same reference numeral, and as such no additional descriptionwill be provided for these elements.

[0087] According to this third preferred embodiment of the invention,however, segmenting logic functions 136 detect differentially encodedcode symbols, also arranged into segments of sixty-four symbols in thisexample. In this embodiment of the invention, the preamble correspondsto a sequence of differences that are maximized for the symbol fromsegment to segment.

[0088] The signal paths in chip-rate demodulation and despreadingfunction 48″ shown in FIG. 9 are identical to those in FIG. 8 forfunction 48′, in this example. This similarity includes segmenting logicfunction 136 ₀ receiving output X(0) from Walsh Hadamard transform andcode correlation function 124 ₀, output X(1) from Walsh Hadamardtransform and code correlation function 124 ₁, output X(2) from WalshHadamard transform and code correlation function 124 ₂, and output X(3)from Walsh Hadamard transform and code correlation function 124 ₃.Similarly, the other fifteen segmenting logic functions 136 ₁ through136 ₁₅ receive their corresponding inputs from each of the WalshHadamard transform and code correlation functions 124, for theircorresponding symbol.

[0089] The function performed by segmenting logic function 136 ₀, inderiving a difference value according to this preferred embodiment ofthe invention, corresponds to:

|X(1)X(0)*+X(2)X(1)*+X(3)X(2)*|

[0090] where the * indicates complex conjugate. The same differenceoperation is performed by each of the other segmenting logic functions136 ₁ through 136 ₁₅ upon their respective inputs. In this manner, theone of segmenting logic functions 136 generating the highest amplitudeoutput based on its difference function will indicate the preamble valuetransmitted, as differentially encoded.

[0091] It is contemplated that these, and other coding and decodingalternative embodiments, may be used in connection with the presentinvention, while still attaining the benefits of efficient computationand realization, with good performance over varying transmissiondistances and mobile unit velocities.

[0092] While the present invention has been described according to itspreferred embodiments, it is of course contemplated that modificationsof, and alternatives to, these embodiments, such modifications andalternatives obtaining the advantages and benefits of this invention,will be apparent to those of ordinary skill in the art having referenceto this specification and its drawings. It is contemplated that suchmodifications and alternatives are within the scope of this invention assubsequently claimed herein.

1-24. (Canceled)
 25. A method of decoding a preamble, comprising thesteps of: extracting a first number of groups of signals having a secondnumber of signals in each group from a data stream having apredetermined length, wherein each group has a third number ofsubgroups; applying one signal from each subgroup to each respectivedespreader circuit of a third number of despreader circuits, eachdespreader circuit producing a respective output signal; and producing afirst number of transforms from the output signal from each respectivedespreader circuit of each subgroup, each transform having the thirdnumber of signals.
 26. A method as in claim 25, comprising summing arespective signal corresponding to each transform at a third number ofsum circuits, thereby producing the third number of sum signals.
 27. Amethod as in claim 26, wherein a product of the first and second numbersis equal to the predetermined length.
 28. A method as in claim 27,wherein the first number is 4, the second number is 1024, the thirdnumber is 16, and the predetermined length is
 4096. 29. A method as inclaim 26, wherein the transform is a Walsh Hadamard transform.
 30. Amethod as in claim 26, wherein the respective signal corresponding toeach transform is a square of the amplitude of the transform signal. 31.A method as in claim 26, wherein the sum signal corresponds to a matchbetween data stream and one of the plurality of codes.
 32. A method asin claim 25, comprising: producing a plurality of products, each productcomprising a respective transform signal and complex conjugates ofanother respective transform signal; and summing a plurality of theproducts at each of a third number of sum circuits, thereby producingthe third number of sum signals.
 33. A method as in claim 22, wherein aproduct of the first and second numbers is equal to the predeterminedlength.
 34. A method as in claim 23, wherein the first number is 4, thesecond number is 1024, the third number is 16, and the predeterminedlength is
 4096. 35. A method as in claim 22, wherein the transform is aWalsh Hadamard transform.
 36. A method as in claim 22, wherein the sumsignal corresponds to a match between data stream and one of theplurality of codes.
 37. A method of decoding a data sequence having agroup of signals repeated a predetermined number of times, comprisingthe steps of: applying one signal from each group to a respectivedespreader circuit of a plurality of despreader circuits, eachdespreader circuit of the plurality of despreader circuits producing arespective output signal; and producing a first number of transformsfrom the output signal from each respective despreader circuit, eachtransform having a second number of signals.
 38. A method as in claim37, wherein the plurality of despreader circuits comprises 64 despreadercircuits.
 39. A method as in claim 37, wherein the first number oftransforms is
 4. 40. A method as in claim 37, wherein each transform isa Walsh Hadamard transform.
 41. A method as in claim 37, wherein theplurality of sum signals corresponds to a match between the group ofsignals and one of the plurality of codes.
 42. A method as in claim 37,comprising summing a respective signal corresponding to each transformat a respective sum circuit, thereby producing a plurality of sumsignals.
 43. A method as in claim 37, comprising: producing a pluralityof products, each product comprising a respective transform signal andcomplex conjugates of another respective transform signal; and summing aplurality of the products at each of a plurality of sum circuits,thereby producing a plurality of sum signals.
 44. A method of encoding apreamble, comprising the steps of: selecting a first code from aplurality of orthogonal codes; repeating the first code a plurality oftimes to produce a sequence having a predetermined length; and combiningthe sequence with a second code having the predetermined length.
 45. Amethod as in claim 44, wherein the plurality of orthogonal codes areWalsh Hadamard codes corresponding to users in a wireless cell andwherein the second code is a scrambling code corresponding to a wirelesscell.